Gasoils or diesels produced from thermal or catalytic cracking processes are known to be unstable. While in storage, they form gums and polymers that can plug burner tips in furnaces or filters in engines. Further, new environmental constraints demand that these fuels reduce their sulphur, nitrogen, water and chlorides contents. Hydrotreating is commonly used in refineries to stabilize gasoils and to remove some of their contaminants. However, hydrotreating processes require high pressures and/or temperatures and the reactors must either be made of, or clad with, high alloy steels to resist hydrogen permeation in the metal walls. There must also be a hydrogen plant or pipeline close by. Because of the high costs of such units, they are only viable as part of refineries or large plants. Also, the hydrotreated oils must be dried to meet water content and appearance specifications.
Used lubricating oils are classified as hazardous products in many countries, mostly because of the additives that they contain. Of all the by-products from the oil industry, used oils pose the greatest danger to the fresh water supply. The Environmental Protection Agency (EPA) states that: “One gallon of used oil can pollute one million gallons of water”. Among the processes to treat used oils for their reuse as fuel, thermal cracking is a viable option for smaller facilities. More precisely, the additives in the used oil must be destroyed and removed. The main product is a wide range diesel or heating fuel. It tends to darken as soon as it comes into contact with air: it is unstable. Also, the wide range diesel has a high sulphur content, 3 or 4 times the 0.1% wt sulphur specification for heating oils in Europe, and has a bad odour.
Processes to stabilize and/or desulphurize diesel fuels produced by cracking heavier oils are well known. In refineries, hydrocracking and hydrotreating processes use hydrogen in catalytic reactors at high temperatures and pressures to achieve clear, stable diesel fuels with good burning characteristics and with sulphur contents as low as 15 ppm that meet ultra-low sulphur specifications. These processes not only require large, heavy reactors made of metals that resist hydrogen permeation, and corrosion, but also require hydrogen production plants or pipelines near-by. They are not suited for small or isolated refineries or used oil applications.
In used oil applications, the UOP Hylube process (U.S. Pat. No. 5,904,838) uses hydrogen at high temperatures and pressures to recycle the feed oil into lubricating oils. Others hydrotreat only the lube oil products, obtained by successive distillations of used oils.
Canadian Patent No. 2,245,025 (Ikura et al.) mentions that gasoil produced by thermal cracking of used oils can be stabilized using methanol extraction.
There are also processes to remove sulphur and/or water from naphtha and other light oils but these are not applicable to diesel fuels. In the solutizer process, Canadian Patents Nos. 456,448 (Border) and 456,599 (Bell et al.) mention that mercaptans and other weak acids contained in sour hydrocarbon distillates, and more particularly in gasoline distillates, would be extracted with solutizer solution, i.e. aqueous solutions of alkali metal hydroxides containing solutizers.
Hassan et al. (Journal of Applied Sciences Research, 5(5); pp. 515-521, 2009) mention that sulphur could be removed from straight run diesel fuel with a mixture of NMP (normal methyl pyridine), ethylene glycol, DMF (dimethyl formamide) and furfural.
Toteva, Topalova, and Manolova (Journal of the University of Chemical Technology and Metallurgy, 42, I, 2007, pp. 17-20) mention that two-stage extraction of diesel fuel with DMF could reduce the aromatics and sulphur (from 2% wt to 0.33% wt) in a non-hydrotreated diesel fuel. This is not enough to meet heating fuel specifications for sulphur of less than 0.1% wt.
U.S. Pat. No. 6,320,090 (Sherman et al.) mentions that DMF could be used as a solvent to remove mostly poly aromatic hydrocarbons (PAH) as well as sulphur and nitrogen compounds from used oils that have been subjected to successive vacuum distillations.
Others have tried solvent extraction processes to remove sulphur compounds from fuel oils.
U.S. Pat. No. 5,753,102 (Funakoshi et al.) uses a mixture of acetone, water and iodine as the preferred solvent to remove sulphur from various straight run oils. They also tested more polarized solvents including DMF, acetonitrile, trimethyl phosphate, nitromethane, methanol, hexamethyl phosphoramide, acetic acid, pyridine, and N-methylperolidinone with less success.
U.S. Pat. No. 5,494,572 (Horii et al.) completes the sulphur removal from oil that has been hydrotreated using organic solvent containing nitrogen, specifically pyridinium salts, with another solvent containing hydroxyl groups, specifically one or more of water, methanol, ethanol, propanol, butanol, ethylene glycol, and glycerol. Hydrotreating is the more costly process.
In the process described by U.S. Pat. No. 5,059,303 (Taylor et al.), oils produced via cracking processes, ranging from cracked naphtha, gasoil and vacuum residue, are contacted with an extraction solvent to reduce their sulphur and nitrogen content prior to hydrotreating. The solvents used are polarized and in an aqueous solution. They include N-methyl pyrrolidone, furfural, DMF, and phenol.
U.S. Pat. No. 4,405,448 (Googin et al.) mention a polar solvent, specifically DMF and water, intended to remove polychlorinated biphenyls (PCB) from transformer oil. A second extraction using a non-polar solvent, chosen from normal pentane to normal octane, is intended to remove the PCB from the polar solvent.
For the past ten years, several oil desulphurization processes use an oxidizing agent and a catalyst to oxidize mercaptans and thiols in the oil. In a second step, polarized solvents are used to extract the sulphur oxides from the oil.
U.S. Pat. No. 6,274,785 (Gore) uses dimethylsulfoxide as the extraction solvent.
Canadian Patent No. 1,287,007 (Kittrel et al.) suggests using solvents having a dipole moment greater than 2, mixed with water, to extract the sulphur and nitrogen oxides from the oil.
U.S. Pat. No. 5,154,817 (Reid) mentions that cracked oils can be stabilized with additive injection. However, additives do not remove mercaptans and thiols from the oil.
The complete solvent regeneration is difficult because the solvents and the oils to treat have similar boiling points and gravities. Solvent losses render these processes impractical.
There was therefore a need for a new process able to stabilize, desulphurize, neutralize and dry wide range diesel, which process being free of at least one of the drawbacks of the prior processes.
There was therefore also a need for a process able to stabilize, desulphurize, neutralize and dry the heating oil to meet the heating oil specifications, which process being free of at least one of the drawbacks of the prior processes.
There was a further need for a process that would also be effective in reducing the sulphur in diesel cuts produced by catalytic or thermal cracking of heavy oils in refineries.
There was particularly a need for a low cost process to stabilize and remove contaminants from wide range diesels or gasoils that can be used in smaller plants, such as used oil cracking units.
There was a further need for new stabilized wide range diesel obtained from an unstable oil.
There was also a need for uses of a stabilized and/or desulphurized wide range of diesel.